U.S. Pat. No. 5,886,822 discloses an ophthalmic lens presenting a projection insert. Such a projection insert is constituted by an optical imager for shaping light beams from an electronic and optical system for generating light beams from an electronic signal, of the miniature screen, laser diode, or light-emitting diode (LED) type. The optical imager directs the light beams towards the eye of the wearer so as to enable the information content thereof to be viewed.
An example of a known display is shown diagrammatically in greater detail in FIG. 1.
By way of example, the optical imager is of the same type as that described in above-mentioned U.S. Pat. No. 5,866,822.
An electronic signal carrying information is taken to a miniature screen 1 by a cable 7. Using this signal, the miniature screen 1, illuminated by a back projector, generates a pixellized image corresponding to the information. By way of example, it is possible to use a “Kopin Cyberdisplay 320 color” screen that generates 320×240 pixels and that has dimensions of 4.8 millimeters (mm)×3.6 mm. The screen 1 is put in a referenced position relative to the optical imager 5 by means of a mechanical interface. A protective housing protects all or part of the assembly. Optical components 8, here a mirror and a lens, are associated with the screen 1.
That optical imager 5 also includes a propagation prism 5a, a counter-prism 5b, a quarterwave plate 5c, and a spherical Mangin mirror 5d. A spherical Mangin mirror is a planospherical lens in which the spherical face has been made reflective by aluminum or equivalent treatment.
The imager 5 also has polarization separation treatment 6 that can be implemented in the form of depositing thin layers, either on the propagation prism 5a, or on the counter-prism 5b, or by means of a film adhesively bonded between two of the above-mentioned elements.
That imager 5 is embedded in a lens 9 and the housing faces the rear of the lens, with reflecting treatment 5e then being included in the lens. On the same principle, the housing could be disposed to one side of the lens 9, in which the reflecting element 5e is omitted.
The word “lens” is used more particularly for an optionally correcting eyeglass that is designed to be mounted in an eyeglass frame. The ophthalmic eyeglass lens presents conventional functions such as correcting eyesight, and antireflection, antidirtying, antiscratching, treatments, for example.
It is known to fasten the light beam generator system on the lens and also to enable focusing to be adjusted by adjusting the distance at which the information image is viewed, and consequently by setting the viewing distance appropriately to enable the wearer to see a sharp image comfortably by means of the following arrangement. The lens is secured to an adapter constituted by a plate carrying two rods on which the housing of the light beam generator system is slidably engaged. During this adjustment, the housing is engaged to a greater or lesser extent on the slides so as to adjust its distance, and then it is locked in place by a transverse screw.
That type of connection and focus-adjusting device raises the following technical problems.
Depending on the extent to which the housing is engaged, the overall size of the display varies. This can lead to constraints in how it is made.
That type of device inevitably leads to a large amount of slack between the rods and the slides, and that is harmful to the accuracy of the display.
In general, the housing is made of plastics material, while the plate and its rods are made of metal. This results in the housing wearing quickly, thereby further increasing slack and inaccuracy of the housing.
Finally, in that prior art, adjustment is performed manually, in the sense that the wearer needs to take hold of the housing and slide it on the rods until a good focus is obtained. Naturally, such an arrangement is not very accurate and is not very comfortable to use, and in particular it is poorly adapted to everyday use, as opposed to experimental use.
Consequently, it can be envisaged to make a display fitted with a focus-adjustment device operating by adjusting the length of the light beams between the optical elements and the imager, with said adjustment device being included in the light beam generator system, the light beam generator system comprising for example a stationary plate to which at least one of the optical elements is connected via a movable connection that is adjustable by means of an actuator device.
Consequently, the connection between the light beam generator system to the lens does not need to enable distance to be adjusted, but does need to be relatively discreet on the lens for reasons of appearance, while also serving to provide accurate positioning and retention, and also being easier to use.
For this purpose, the invention provides an ophthalmic display comprising:                a generator system for generating light beams;        an optical imager for shaping light beams emitted by a miniature screen of said light beam generator system, which beams are introduced into said imager via an inlet face, and for directing said beams towards the eye of a wearer in order to enable an image to be viewed;        an adapter in a reference position relative to said imager; and        a connection arrangement carried by said light beam generator system for connection to said adapter, the connection between said system and said adapter being releasable;the display being characterized in that said adapter is constituted by at least two magnets for co-operating by the magnetic effect and by interengagement with at least two magnets carried by said connection arrangement.        
The advantage of this type of solution lies in it being well adapted to engaging a light beam generator system on a lens of information eyeglasses while complying with severe constraints mechanically, optically, and in terms of size, weight, and appearance.
The number of parts used is minimized. It can be used without any external tool, swiftly, and easily. The absence of rubbing parts ensures that positioning accuracy is conserved. From the point of view of appearance, the residual parts on the information eyeglass lens, i.e. the two magnets, are very discreet. The overall size of the connection system is minimal, both within the light beam generator system and on the lens. Its contribution to total weight is minimal, given that the parts dedicated solely to connection are the magnets.